The invention relates generally to the storage of data in mass storage systems, and in particular to the ability to access data in a mass storage system from different facilities using different, and often incompatible, filesystem formats.
As data processing systems grow in size and complexity, the ability to access user data from different facilities, or from different systems within the same facility becomes increasingly advantageous. On the other hand, however, different host systems, to the extent they use different operating systems, often have different and incompatible meta-data formats. Thus, when a Unix operating filesystem accesses user data, it uses a file request meta-data format which is different from, for example, a Windows based system access. Further, even when two Unix based systems access the same data, it is possible, and indeed not unlikely, that different host computers, to the extent that they use different versions of Unix, will not be compatible with each other. Accordingly, it would be advantageous to enable different operating systems to share the same user data even though those operating systems themselves had incompatible meta-data formats. This would provide the advantage of enabling a single copy of the user data to be easily used, updated, modified, etc., by users irrespective of the host operating system and filesystem, in a manner which is simply not practically available today.
There do, however, exist several data sharing systems. In one system, data is shared by keeping multiple copies of the user data, with the copies being periodically updated so they are synchronized to each other. This requires two copies of the data which will be more expensive because of the data storage space required. A second form of data sharing provides that two hosts, running the same operating system or xe2x80x9crawxe2x80x9d device, access the user data where only one host can access the user data at the time. This requires, then, that the two hosts be limited to the same operating system or filesystem.
A third system, providing for so-called concurrent access, typically uses a distributor lock master and can be used in a clustered filesystem using a custom format. This system gets quite complex, and provides for inefficient CPU and network usage.
Accordingly, a more efficient and flexible system would be desirable to share the data without the need for special operating systems. This would enable different operating systems to access the same single copy of user data.
The invention relates to an apparatus and method for accessing storage from at least two different host computers having different operating system meta-data formats. The method of the invention features the steps of creating a first file having a first meta-data format and user data blocks in the mass storage memory, using a first host computer, reading a logical to physical mapping of the user data blocks from the first file, creating a second file having a second meta-data format using a second host computer, with the second file having blocks preallocated to be the same length as user data blocks of the first file, retrieving a logical to physical mapping of the preallocated blocks, and linking the data blocks of the preallocated file to the data blocks of the first file.
In an alternate embodiment, the method of the invention provides for indirectly storing data blocks from a computer and features the steps of creating a meta-data file identifying a file specification data, setting an indirect storage flag in the meta-data, writing in user data blocks an address identifying the corresponding indirectly stored data blocks, and accessing the indirectly stored datablocks using the indirect addresses.